The process of xerography includes forming a light image of an original document to be copied typically recorded in the form of a latent electrostatic image upon a photosensitive or a photoconductive member, with subsequent rendering of the latent image visible by the application of toner compositions. The resulting visual toner image can be either fixed directly upon the photosensitive member or the photoconductor member, or transferred from this member to a support member, such as a sheet of plain paper, with subsequent affixing by, for example, the application of heat and pressure of the developed image thereto.
To affix or fuse toner material onto a support member like paper, by heat and pressure, it is usually necessary to elevate the temperature of the toner and simultaneously apply pressure sufficient to cause the components of the toner to become tacky and coalesce. In both the xerographic and the electrographic recording arts, the use of thermal energy for fixing toner images onto a support member is known.
One approach to the heat and pressure fusing of toner images onto a support member has been to pass the support member, with the toner images thereon, between a pair of pressure engaged roller members, at least one of which is internally heated. For example, the aforementioned support member containing developed toner images may pass between a fuser roller and a pressure roller. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rollers with the toner image contacting the fuser roll to thereby cause heating of the toner images within the nip.
The process of transferring charged toner particles from an image bearing member marking device, such as a photoconductor, to an image support substrate, like a sheet of paper, involves overcoming cohesive forces holding the toner particles to the image bearing member. The interface between the photoconductor surface and image support substrate may not in many instances be optimal, thus, problems may be caused in the transfer process when spaces or gaps exist between the developed image and the image support substrate. One aspect of the transfer process is focused on the application and maintenance of high intensity electrostatic fields in the transfer region for overcoming the cohesive forces acting on the toner particles as they rest on the photoconductive member. Control of these electrostatic fields and other forces is a factor for inducement of the physical detachment and transfer of the charged toner particles without scattering or smearing of the toner particles. Mechanical devices that force the image support substrate into contact with the image bearing surface have also been incorporated into transfer systems.
More specifically, the process of transferring charged toner particles from an image bearing member, such as a photoconductive member, to an image support substrate, such as a copy sheet or sheet of paper, may be accomplished by overcoming adhesive forces holding the toner particles to the image bearing member. In general, the transfer of developed toner images in xerographic processes has been accomplished by electrostatic induction using a corona generating device, wherein the image support substrate is placed in direct contact with the developed toner image on the photoconductive surface while the reverse side of the image support substrate is exposed to a corona discharge. The corona discharge generates ions having a polarity opposite that of the toner particles, thereby electrostatically attracting and transferring the toner particles from the photoconductive member to the image support substrate.
In the electrostatic transfer of the developed toner image to a copy sheet, it is usually necessary for the copy sheet to be in uniform intimate contact with the toner image developed on the photoconductive surface. Unfortunately, the interface between the photoreceptive surface and the copy sheet is not always optimal. Thus, non-flat or uneven image support substrates, such as copy sheets that have been mishandled, left exposed to the environment or previously passed through a fixing operation, such as heat and/or pressure fusing, tend to promulgate imperfect and partial contact with the photoreceptive surface of the photoconductor. Further, in the event the copy sheet is wrinkled, the sheet will not be in intimate contact with the photoconductive surface and spaces, or air gaps will materialize between the developed image on the photoconductive surface and the copy sheet. Problems may occur in the transfer process when spaces or gaps exist between the developed image and the copy substrate, and where there is a tendency for toner not to transfer across these gaps causing variable transfer efficiency, and which can create areas of low or no transfer resulting in a phenomenon known as image transfer deletion. Image deletion is very undesirable in that useful information and indicia are not reproduced on the copy sheet.
Image transfer deletion is undesirable in that portions of the desired image may not be appropriately reproduced on the print sheet. The area of the transfer assist blade that contacts the photoreceptor will, in most instances, pick up residual dirt and toner from the photoreceptor surface. In the next sequence, print sheets, such as those used with xerographic systems, will cause the residual dirt on the transfer assist blade to be transferred to the back side of the print sheet resulting in unacceptable print quality defects. Additionally, continuous frictional contact between the blade and the photoreceptor, also referred to in many instances as a photoconductor, may cause permanent damage to the photoreceptor.
In single pass color machines, it is desirable to cause as little disturbance to the photoreceptor as possible so that motion errors are not propagated along the belt to cause image quality and color separation registration problems. One area that has potential to cause such a disturbance is when a sheet is released from the guide after having been brought into contact with the photoreceptor for transfer of the developed image thereto. This disturbance, which is often referred to as trail edge flip, can cause image defects on the sheet due to the motion of the sheet during transfer caused by energy released due to the bending forces of the sheet. Particularly in machines which handle a large range of paper weights and sizes, it is difficult to include a sheet guide which can properly position any weight and size sheet while not causing the sheet to oscillate after having come in contact with the photoreceptor.
For multicolor xerography, it is desirable to use an architecture which comprises a plurality of image forming stations and a transfer assist member that can cause image deletions. One example of the plural image forming station architecture utilizes an image-on-image (IOI) system in which the photoreceptive member is recharged, reimaged and developed for each color separation.
There is a need for transfer assist members that substantially avoid or minimize the disadvantages illustrated herein.
There is also a need for toner developed images transfer assist members that permit the continuous contact between a photoconductor and the substrate to which the developed toner image is to be transferred, and processes for enhancing contact between a copy sheet and a developed image positioned on a photoconductive member.
Further, there is a need for transfer assist members (TAM), such as a transfer assist blade (TAB), comprising a low surface energy check film with excellent rub resistance for extended time periods, and where the TAM further includes a wear resistant top layer.
Another need resides in the provision of check films with improved rub resistance compared, for example, to known thermoplastic polyester check films.
Also, there is need for transfer assist members comprising fluoro containing polymers that are environmentally acceptable, and that are free of, or possess minimal bioaccumulation characteristics.
Further, there is a need for environmentally acceptable fluoropolymer based check films for inclusion into transfer assist members, and which fluoro polymer is free of, or substantially free of bioaccumulation characteristics, are readily soluble in alcohol solvents, thereby permitting efficient processes for achieving environmentally acceptable check films, and which fluoropolymers have obtained regulatory approvals from agencies such as the US, EPA, the UK Health and Safety Executive and Environmental Agency, METI in Japan and in Canada are REACH compliant.
Yet another need resides in providing xerographic printing systems, inclusive of multi-color generating systems, where there is selected a transfer assist member that maintains sufficient constant pressure on the substrate to which a developed image is to be transferred, and to substantially eliminate air gaps between the sheet and the photoconductor in that the presence of air gaps can cause air breakdowns in the transfer field.
Moreover, there is a need for transfer assist members that enable suitable and full contact of the developed toner image present on a photoconductor, and a substrate to which the developed image is to be transferred.
Additionally, there is a need for transfer assist members that contain durable compositions that can be economically and efficiently manufactured, and where the amount of energy consumed is reduced.
Yet additionally, there is a need for a multilayered transfer assist member that includes as one layer a check film on the side exposed to a dicorotron/corona element, and which member possesses excellent resistance characteristics.
Also, there is a need for transfer assist members where the check film layer can be generated roll to roll by economic extrusion processing.
Further, there is a need for transfer assist members with a combination of excellent durability, that exert sufficient constant pressure on a substrate and permit the substrate to fully contact the toner developed image on a photoconductor, and where complete transfer to a sheet of a developed image contained on a photoconductor results, such as for example, about 90 to about 100 percent, from about 90 to about 98 percent, from about 95 to about 99 percent, and in embodiments about 100 percent of the toner image is transferred to the copy sheet or other suitable substrate, and wherein blurred final images are minimized or avoided.
There is moreover a need for a transfer assist member, such as a transfer assist blade, that sweeps the backside of the image support substrate with a constant force at the entrance to the transfer region, and itself does not contact the photoconductor.
Moreover, there is a need for composite transfer assist blades that overcome or minimize the problems associated with a single component blade, as a single component blade in order to be flexible enough to prevent image damage often does not provide enough contact force to the back of the sheet to enable complete image transfer thus giving rise to transfer deletions and color shift. When a thick enough blade is used, the stress on the single blade material is very high and thus subject to breaking.
Yet, there is another need for transfer assist members that include check films, and which members are useful in electrophotographic imaging apparatuses, including digital printing where the latent image is produced by a modulated laser beam, or ionographic printing where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
Also, there is a need for transfer assist members that are wear resistant, and that can be used for extended time periods without being replaced.
In addition, there is a need for transfer assist members that contain components that are substantially free of bioaccumulation unlike known main-chain perfluoroalkyl compounds/resins that tend to bioaccumulate.
These and other needs are achievable in embodiments with the transfer assist members and components thereof disclosed herein.